摩擦与滚阻对被动行走器步态影响的研究

本文研究了圆弧足被动行走器支撑足与地面间的摩擦系数和滚阻系数对被动行走器步态的影响. 首先分别利用扩展的 赫兹接触力模型和LuGre摩擦模型描述了支撑足与地面接触点处的法向支撑力和切向摩擦力,并考虑了行走过程中支撑足 所受的滚动摩阻;其次利用第二类Lagrange方程推导出了该系统的动力学方程,并通过与已有成果的对比确定 了合适的LuGre摩擦模型参数;最后仿真分析了摩擦系数和滚阻系数对被动行走器步态的影响. 研究发现:摩擦系数的改变 虽然对被动行走器行走的平均速度、步幅,以及支撑足接触点处的最大法向接触力的影响较小,但摩擦系数的减小 会改变其行走步态类型,如发生倍周期分岔甚至混沌现象;然而,滚阻系数的改变会对行走器行走的 平均速度、步幅,以及支撑足接触点处的最大法向接触力的影响较大,尚未发现滚阻系数的改变会引起其行走步态的变化. 

STUDY ON THE INFLUENCE OF FRICTION AND ROLLING RESISTANCE ON THE GAIT OF PASSIVE DYNAMIC WALKER 1)

In this paper, the influences of friction coefficient and rolling resistance coefficient on the gait of a passive dynamic walker with round feet are studied. Firstly, the normal forces and frictional forces acting on the feet of the passive dynamic walker are described based on a modified Hertz contact model and LuGre friction model, and the rolling friction resistance of the supporting foot during walking was also considered. Secondly, the dynamic equations of the passive dynamic walker are obtained by using Lagrange's equations of the second kind, and the appropriate parameters of LuGre friction model are selected by comparing with the previous studies. Finally, the influence of friction coefficient and rolling resistance coefficient on the gait of passive dynamic walker are simulated and analyzed. It is found that although the change of friction coefficient has little effect on the average speed, stride and the maximum normal contact force at the contact point of the supporting foot, the reduction of friction coefficient will change the gait types, such as periodic doubling motion or chaotic motion. However, the change of the rolling resistance coefficient will lead to a great difference on the average speed, stride and the maximum normal contact force at the contact point of the supporting foot, but it has not been found that the change of rolling resistance coefficient will cause the change of the walker's gait types.